ATMOsphere America 2014: state of the art low charge ammonia industrial refrigeration technologies

ammonia21.com reports on industry perspectives and trends regarding ammonia based industrial refrigeration systems presented by key manufactures during the highly successful ATMOsphere America 2014 event, which took place on 18-19 June, in San Francisco, California. Reducing refrigerant charge remains top of the agenda, alongside improving efficiency and keeping costs low. In part 1 of ammonia21.com’s ATMOsphere reporting main case study findings presented by Azane, Colmac Coil and Alfa La

Organised for the first time in San Francisco, California, ATMOshpere America 2014 gathered leading ammonia refrigeration system manufacturers, who presented their very latest ammonia and CO₂/ammonia cascade refrigeration solutions through case studies and comparative analyses.

Low charge ammonia - the natural replacement for R22

Derek Hamilton, US Business Development Manager for Azane, discussed the effects of the R22 phase-out timetable published by the US EPA, according to which the manufacturing of R22 will no longer be possible in the US after 2020. For Hamilton non-action is not an option for end users, since non-compliance will necessarily result in financial penalties. He also pointed out that there are lessons to be learned from the European market, where as from 1 January 2015 it will be illegal to use recycled or reclaimed HCFCs, such as R22, to service RAC equipment.

Exploring alternative solutions, Hamilton positioned himself against drop-in replacements and new HFC systems, arguing that the former face technical challenges regarding capacity, leakage rate and oil compatibility, whilst the latter face sustainability challenges. “Natural refrigerant is the option!” Hamilton said.

In the US, Azane offers a low charge, air-cooled packaged ammonia chiller that is factory built and tested. These chiller packages dramatically reduce installation costs, as evidenced by an Azane installation at a Dairy facility in Puerto Rico. Azane worked in close collaboration with the dairy to design a 190TR package consisting of a central cooling system, air-handling units and twin-screw compressors. Ammonia’s excellent thermodynamic efficiency resulted in energy efficiency savings amounting of almost USD41,000 (EUR30,000) per year.

Using direct expansion ammonia system to reduce refrigerant charge below 10,000 lbs (4,500 kg)

Bruce Nelson, President of Colmac Coil Manufacturing introduced his presentation by discussing pumped ammonia systems, which historically have been very popular due to their simple operation and good evaporator performance over a wide range in load, regardless of temperature. However, pumped ammonia maximizes the amount of refrigerant in the evaporators.

To address this issue, Colmac Coil manufactures direct expansion (DX) systems that reduce the charge in the evaporators by 30 - 50 times, and reduce the system charge by 4 - 5 times, allowing the ammonia charge to be kept below 10,000 lbs threshold (4536 kg) for systems ranging between 1500 TR and 1800 TR. In addition, DX improves energy efficiency and lowers power consumption.

A direct expansion ammonia system to a public refrigerated warehouse with a total area of 403,000 sq ft (37,500 sq m) and a total refrigeration load of 1,007 TR had an installed cost approximately USD200,000 (EUR147,000) lower than for a pumped system. What is more, thanks to the Colmac Coil installation, which keeps the refrigerant charge below the10,000 lbs threshold (4536 kg), the facility will not be listed in the federal National Emphasis Program.

The warehouse comprises:

Freezer and convertible rooms operating at -23.3°C with a 801 TR refrigeration load
USDA room and loading dock operating at +4.44 °C with a 206 TR refrigeration load
Central engine room with thermosyphon oil cooling economized screw compressors
Ammonia distribution system with flash gas and external control valves

Pros and cons of Low Charge CO₂/ammonia cascade system

Presenting the advantages and disadvantages of CO₂/ammonia cascade systems, Carnie Marsh, National Key Accounts Manager at Alfa Laval, highlighted that cascade CO₂/ammonia systems reduce the ammonia charge, have lower operational costs and higher energy savings than conventional two-stage ammonia systems. This is true for low temperature CO₂ circuits operating at -58°F (-50°C) to 20°F (-6.67°C). On the other hand, such systems require higher working pressures at moderate temperatures, and typically electric defrost.

Ammonia refrigerant charge reduced by 2-3 times using Alfa Laval’s semi-welded plate heat exchanger

Marsh went on to talk about Alfa Laval’s upgraded semi-welded plate heat exchanger with a UTurn(p)TM ammonia flooded separator, which features new pressure design, a new gasket development for both refrigerants and a more compact, lower charge design flooded separator vessel. The semi-welded units can only exhibit external leakages, reducing the risk that ammonium carbonate will contaminate the system, as is the case in all-welded systems.

Marsh concluded his presentation with the findings of a comparative analysis of the ammonia charge of various cascade systems. The data, collected on the basis of a CO₂ low tempareture system (-50°C) with a load of 1380 MBH, with CO₂ condensing at -17.8°C and flooded ammonia cooling evaporator at 23.2°C revealed the following:

Flooded shell & tube: 210 lbs ammonia (95.3 kg)
Shell & plate: 175 lbs ammonia (79.4 kg)
Semi-welded plate heat exchanger with conventional separator vessel: 146 lbs Ammonia (66.2 kg)
Semi-Welded Plate Heat Exchanger with a UTurn(p)TM separator: 26 lbs ammonia (11.8 kg)

The results show the semi-welded plate heat exchanger with a UTurn(p)TM separator requires the lowest charge among all systems: 26 lbs (11.8kg).

U-Turn separator reduces refrigerant charge and energy consumption

The U-Turn was also discussed by Rolf Christensen Manager, Product Portfolio Management from Alfa Laval, who presented the workings of this innnovative technology. U-turn separators go beyond the conventional gravity separator to a separation by centrifugal forces, using a design that allows for high separation efficiency, and is low weight and compact.

Reporting on the energy consumption benefits of the U-turn, Christensen presented data from a 142TR (500kW), single stage system operating in San Francisco. He calculates that the U-turn can achieve savings of USD10,000 (EUR7,348) annually, by reducing electricity consumption by 73 MWh.

In another installation at Homerton University Hospital in the UK an existing R22 system was upgraded from 97 to 142 TR (from 340 to 500 kW). The charge dropped from 551lbs (250 kg) of R22 to 110lbs (50kg) of NH3, in the new system. As a result, the capacity was increased by 50% and the charge reduced from 5.7 to 0.77 lbs/TR (from 0.74 to 0.1 kg/kW).